Microneurosurgery is defined as neurosurgery done using operative magnification. The application of microsurgical techniques to the treatment of brain tumors and cerebro-vascular disease was recently ranked in a study of surgical services in the United States by the American College of Surgeons and the American Surgical Association among the first order research advances in surgery in the last 25 years. The accurate use of surgical magnification for neurosurgery requires an understanding of the surgical anatomy not visible to the naked eye. The main focus of this research has been toward charting the anatomy of small brain arteries which, at surgery done with the naked eye, might be occluded in the treatment of ballooned ruptured weak areas of the cerebral vessels. Occlusion of these small arteries at the time of surgical obliteration of the weak spots often causes paralysis, speech loss or loss of life. Similar studies of neural structures are increasing the accuracy with which nerves and brain tissue can be preserved at surgery done with magnification.